Methodology.
This page explains how we place every statement: which grade of evidence it receives, how we judge transferability between species, and where the limits of our own system lie.
An internal grid, not a global standard
The scales below are editorial tools. They help us to phrase statements consistently and to make visible to readers what a statement rests on. They are not a validated clinical assessment instrument and they do not replace a formal evidence appraisal by established methods.
Evidence grades
| Grade | What it means | Typical basis |
|---|---|---|
| A | Robust, consistent evidence | several good studies pointing the same way, or one high-quality systematic review |
| B | Moderate evidence with visible limitations | sound studies, but few in number, short in duration or narrow in population |
| C | Weak or inconsistent evidence | small samples, contradictory findings, high risk of bias |
| D | Mechanistic or exploratory data | cell experiments, animal models without a clinical endpoint, pilot studies |
| E | Opinion, experience, hypothesis | expert opinion, individual cases, unpublished observation |
| NA | Not applicable | the page deals with a method or a term, not with a question of effect |
Transferability between species
The second scale answers a different question. Not: how good is the study? But: who does its result apply to? A faultless study in rodents remains a study in rodents.
| Level | Meaning | What may follow from it |
|---|---|---|
| T0 | No transfer defensible | nothing; the finding holds only in the species studied |
| T1 | Shared mechanism plausible, clinical effect not demonstrated | a hypothesis and a research question |
| T2 | Consistent findings across several models, target data limited | a reasoned expectation, not a conclusion for action |
| T3 | Data in the target species available, but still insufficient | a provisional assessment with an explicit reservation |
| T4 | Effect tested directly in the target species and target population | a statement about that population, still without any individual recommendation |
| NA | No cross-species comparison | the page compares no species |
The six dimensions behind the level
The transferability level comes out of six questions that we work through for every comparative page. The weights make our priorities visible; they are an aid to judgement, not a measurement.
| Dimension | Weight | Guiding question |
|---|---|---|
| Physiological proximity | 20 per cent | Is the organ system built and regulated comparably in both species? |
| Mechanistic agreement | 20 per cent | Does the pathway really run the same way, or is it merely named alike? |
| Consistency of results | 20 per cent | Do the studies in both species point the same way? |
| Comparability of exposure | 15 per cent | Are the amount, the duration and the route of intake comparable at all? |
| Methodological quality | 15 per cent | How high is the risk of bias in the underlying work? |
| External validity | 10 per cent | Does the population studied match the population being talked about? |
What we never do
- convert a dose from one species to another, not even by body weight
- present an association as a cause
- infer a clinical effect from a cell experiment
- cite a finding in the horse as proof in the human being, or the other way round
- assign a grade of evidence without having read the source’s own conclusion
How a page comes about
- Sharpen the question: which species, which population, which endpoint.
- Search the primary literature, systematic reviews and controlled trials first.
- Structured extraction: design, sample, intervention, result, funding, limitations.
- Check every statement against the source’s actual conclusion, not against its title.
- Calibrate the verbs to the strength of the evidence.
- Assign the grade of evidence and the transferability level.
- Language check and, for health-related content, specialist counter-reading.
- Publication with the review date and the due date of the next review.
Review cycle
| Type of content | At the latest after |
|---|---|
| Emergency, warning signs, care | 12 months |
| Human or animal health | 18 months |
| Nutrition | 18 months |
| Methodology | 24 months |
| Study entry | on correction or retraction of the publication |
| Glossary | 30 months |
The evidence letter
Once a month: new syntheses, checked studies, and what has changed in the state of the evidence.